Fix up remove Wakeup preferences

Follow the bug fix addressed in http://review.cyanogenmod.org/#/c/43544/

This fix the issue both Home key wake and Volume rocker wake preferences will be displayed
if either of them activated in device config.

If both of them are not activated it looks fine because eventually Wakeup category
itself removed,though.

Change-Id: I28b7b45d209c3beb9559ed9e7b89612bf8df8bab

Conflicts:
	src/com/android/settings/DisplaySettings.java